/**
 * Persian Calendar see: http://code.google.com/p/persian-calendar/
   Copyright (C) 2012  Mortezaadi@gmail.com
   PersianCalendarUtils.java
   
   Persian Calendar is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation, either version 3 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
package com.sahandrc.calendar.utils;

/**
 * algorithms for converting Julian days to the Persian calendar, and vice versa are adopted
 * from <a href="casema.nl/couprie/calmath/persian/index.html">couprie.nl</a>
 * written in VB.
 * The algorithms is not exactly the same as its original.
 * I've done some minor changes in the sake of performances and
 * corrected some bugs.
 * 
 * @author Morteza  contact: <a href="mailto:Mortezaadi@gmail.com">Mortezaadi@gmail.com</a>
 * @version 1.0
 *
 */
public class PersianCalendarUtils {
    
    /**
     * Converts a provided Persian (Shamsi) date to the Julian Day Number
     *  (i.e. the number of days since January 1 in the year 4713 BC).
     *  Since the Persian calendar is a highly regular calendar, converting to and from a Julian Day Number
     *   is not as difficult as it looks. Basically it's a mather of dividing, rounding and multiplying.
     *   This routine uses Julian Day Number 1948321 as focal point, since that Julian Day Number
     *    corresponds with 1 Farvardin (1) 1. 
     * @param year int persian year
     * @param month int persian month
     * @param day int persian day
     * @return long
     */
    public static long persianToJulian(long year, int month, int day) {      
        return 365L * ((ceil(year - 474L, 2820D) + 474L) - 1L)
                + ((long) Math.floor((682L * (ceil(year - 474L, 2820D) + 474L) - 110L) / 2816D))
                + (PersianCalendarConstants.PERSIAN_EPOCH - 1L)
                + 1029983L * ((long) Math.floor((year - 474L) / 2820D)) 
                + (month < 7? 31 * month: 30 * month + 6 ) + day;
    }
    
    
    
    
    /**
     * Calculate whether current year is Leap year in persian or not
     * @return boolean
     */
    public static boolean isPersianLeapYear(int persianYear) {
        return PersianCalendarUtils.ceil((38D
                +(PersianCalendarUtils.ceil(persianYear - 474L, 2820L) + 474L)) * 682D, 2816D) < 682L;
    }

    /**
     * Converts a provided Julian Day Number
     * (i.e. the number of days since January 1 in the year 4713 BC) to the Persian (Shamsi) date.
     * Since the Persian calendar is a highly regular calendar, converting to and from a Julian Day Number
     * is not as difficult as it looks. Basically it's a mather of dividing, rounding and multiplying.
     * @param julianDate
     * @return long
     */
    public static long julianToPersian(long julianDate) {
        long persianEpochInJulian = julianDate - persianToJulian(475L, 0, 1);
        long cyear = ceil(persianEpochInJulian, 1029983D);
        long ycycle = cyear != 1029982L? ((long) Math.floor((2816D * (double)cyear + 1031337D)/ 1028522D)): 2820L;
        long year = 474L + 2820L * ((long) Math.floor(persianEpochInJulian / 1029983D)) + ycycle;
        long aux = (1L + julianDate) - persianToJulian(year, 0, 1);
        int month = (int)(aux > 186L? Math.ceil((double)(aux - 6L) / 30D) - 1: Math.ceil((double)aux / 31D) - 1);
        int day = (int)(julianDate - (persianToJulian(year, month, 1) - 1L));
        return (year << 16) | (month << 8) | day;
    }
    

    /**
     * Ceil function in original algorithm
     * @param double1
     * @param double2
     * @return long
     */
    public static long ceil(double double1, double double2) {
        return (long) (double1 - double2 * Math.floor(double1 / double2));
    }
    
  
    

  
}
